1. Field of the Invention
The present invention relates to photovoltaic arrays and methods of manufacturing photovoltaic arrays. More particularly, the present invention relates a method of manufacturing solar arrays that requires less time and labor efforts and, therefore, reduced costs.
2. Description of Related Art
Many modern systems, both earth borne and space borne, may use photovoltaic (PV) arrays as either a primary or a secondary power source. For example, certain remotely located systems that are not near the electric power grid rely on a PV array to provide a primary or secondary source of power during daylight hours. Additionally, spacecraft and manmade satellites may use PV arrays not only for operation and recharging of systems during non-eclipse periods but also to augment electrically assisted propulsion and station keeping systems.
There are two types of solar cells currently used to make PV arrays. These types are amorphous semiconductors and single crystal semiconductors. Both amorphous and single crystal semiconductors can be, and have been, used in both earth borne and space borne applications. However, driven by the need to keep size and mass to a minimum, space borne applications use single crystal semiconductors, since these provide conversion efficiencies that presently exceed 25% whereas amorphous semiconductors provide efficiencies of approximately 10%.
The semiconductor material used to form single crystal solar cells is first grown as a cylinder. It is then sliced into wafers, polished, and appropriately doped. Individual cells are then cut from the wafer, and a layer of metal is applied to portions of both the top and bottom surfaces of each cell.
Presently, the most common and commercially accepted method for manufacturing a PV array uses as one of the first steps, forming each solar cell into a so-called xe2x80x9cCell-Interconnect-Coverglass,xe2x80x9d or CIC. To form a CIC, one or more interconnect members made of a thin ribbon of silver or similar metal is either welded or soldered to the solar cell""s top surface metal layer. Thereafter, a liquid, translucent silicone adhesive is applied to the solar cell""s top surface to bond a layer of doped glass to the cell and interconnect.
After all of the solar cells have been formed into CICs, the CICs are assembled into strings. As part of this assembly process, all of the CICs are placed, one at a time, on an alignment tool or jig, with their glass sides down, interleaving the CICs such that the interconnect member from one CIC is resting on the bottom side of an adjacent CIC. The interconnect members are then attached to the bottom side of adjacent CICs by a soldering and/or a welding process. After a desired number of CICs have been so arranged and attached to form a string, the string is transferred to a substrate, which embodies the final solar array configuration. This transfer process is accomplished by first attaching masking tape or similar non-permanent adhesive to the backside of the string, and transporting the taped string, glass side down, onto a transfer device that is fabricated from a sheet of mylar. The transfer device, fabricated from mylar or similar material, allows the array of modules to be handled and lifted into position.
Thereafter, the surface of the substrate to be laminated with the string of solar cells is primed by painting a silane material on the substrate surface. The backsides of each of the solar cells are also primed with this material to promote subsequent silicone adhesion. A thin layer of liquid silicone adhesive, such as uncured (wet) RTV (room temperature vulcanizing) is then applied to the primed substrate. While the RTV is still wet and uncured, the string is quickly set into place atop the RTV applied to the substrate.
The string is aligned and then, to allow even and sufficient bonding of each solar cell, is either weighted or xe2x80x9cbaggedxe2x80x9d until the RTV cures, which takes approximately seven days. If the string is weighted, individual weights are placed atop each of the cells until the RTV cures. If the string is bagged, the substrate is placed into an airtight bag and a vacuum is drawn in the bag, such that typically a one pound per square inch pressure is uniformly distributed on the string, and is maintained until the RTV cures. After the RTV cures, any excess is removed from the PV array.
The aforementioned process was developed in an effort to create a batch process. As noted, first the CICs are assembled, then strings are assembled, and then the strings are transferred to substrates to form the PV arrays. This manufacturing process results in the handling of the solar cells during at least four separate operations. This results in excessive cost and cycle time. In addition, the process permits only portions of the assembly to be automated. Furthermore, because the solar cells are interconnected by soldering or welding, the inevitable need to replace damaged cells on a completed PV array potentially creates extensive difficulty, increased expense, and schedule delays. Typically, 5% to 8% of the solar cells are damaged during this process, adding to the overall cost. In addition, the present process of manufacturing a PV array suggests that the array be assembled in a central manufacturing facility and then either transported to the place of its end use for installation, or the end use system transported to the manufacturing facility for installation.
Hence, there is a need in the art for a method of manufacturing a PV array that is less labor intensive, and thus less costly, while still meeting the operability requirements for both earth borne and space borne environments. Furthermore, there is a need in the art for a PV array, and a method of manufacturing a PV array, that provides the ability to readily repair and-replace PV array components, as necessary. There is additionally a need in the art for a method of manufacturing a PV array that is not constrained to a centralized manufacturing facility, but that provides for in-situ manufacture at the location of the PV array""s end use. There is also a need in the art for a PV array, and a method of manufacturing a PV array, that does not use leaded solar cells.
The present invention is directed toward overcoming the above-noted problems. Namely, the present invention eliminates the need to solder or weld interconnects to cells. In addition, the present invention eliminates the need to prefabricate CICs or strings, and provides for the ability to readily repair and replace damaged solar cells or other array components. Due to the laminar nature of the manufacturing process of the present invention, automation by a simple pick and place process can be fully utilized to facilitate this invention, as opposed to existing methods, which utilize automation to a limited extent.
In one aspect of the present invention, a method of manufacturing a photovoltaic array includes providing a substrate having an array surface, and individually bonding a plurality of solar cells to the array surface with strips of a first double-sided pressure sensitive adhesive tape. Each of the solar cells comprises a negative terminal portion and a positive terminal portion. A plurality of electrically conductive interconnect members are bonded to the array surface with strips of a second double-sided pressure sensitive adhesive tape. Each of the interconnect members having a first and a second end portion. The first end portion of each interconnect member is electrically coupled to the negative terminal of one of the solar cells and the second end portion of each interconnect member is electrically coupled to the positive terminal of an adjacent solar cell. Thus, the plurality of solar cells are electrically coupled in series with one another.
In another aspect of the present invention, a method of manufacturing a photovoltaic array that includes N solar cells electrically coupled in series, each of the N solar cells having a first polarity terminal and a second polarity terminal, includes the step of providing a substrate including an array surface. A first of the N solar cells is bonded to the array surface with a strip of a first double-sided pressure sensitive adhesive tape. A plurality of electrical interconnect members is provided, each including first and second end portions and an intermediate portion. The first end portion of one of the electrical interconnect members is abutted against the first polarity terminal of the first solar cell and the intermediate portion of the first electrical interconnect member is bonded to the array surface with a strip of a second double-sided pressure sensitive adhesive tape. The second polarity terminal of an additional one of the N solar cells is abutted against the second end portion of the previously bonded electrical interconnect member and is bonded to the array surface with a strip of the first double-sided pressure sensitive adhesive tape. The first end portion of an additional one of the plurality of electrical interconnect members is abutted against the first polarity terminal of the additional one of the N solar cells, and the intermediate portion of this additional interconnect member is bonded to the array surface with a strip of the second double-sided pressure sensitive adhesive tape. The previous two steps are repeated until all N of the solar cells are electrically coupled in series.
In yet another aspect of the present invention, a photovoltaic array includes a substrate, a plurality of solar cells, and a plurality of interconnect members. The substrate includes an array surface. The plurality of solar cells each have a negative electrical terminal and a positive electrical terminal and are individually coupled to the array surface with strips of a first double-sided pressure sensitive adhesive tape. The plurality of electrically conductive interconnect members each have a first end portion and a second end portion and are individually coupled to the array surface with strips of a second double-sided pressure sensitive adhesive tape. The first end portion of each interconnect member is electrically coupled to the positive terminal of one of the solar cells and the second end of each is electrically coupled to the negative terminal of an adjacent solar cell, thereby electrically coupling adjacent solar cells in series with one another.